1. Field of the Invention
The invention relates to liquid flow distribution screens and particularly to those that may be used as a membrane support and spacer in electrodialysis cells and similar apparatus.
2. Description of the Prior Art
In electrodialysis cells there is a requirement for membrane supports which also provide for liquid or electrolyte flow and contact with the membrane. These supports should be constructed so that there is maximum contact between the electrolyte and the membrane. The supports must additionally provide separation between one membrane and another or between a membrane and electrode to a very close tolerance in order to insure the highest possible efficiency of operation.
A number of devices exist in the prior art for the purposes described. In some, the flow device is fed with electrolyte over its entire length as is illustrated in U.S. Pat. No. 2,735,812, VanHoek. In that patent, corrugated sheets having a multiplicity of perforations are disclosed as membrane supports. In another, U.S. Pat. No. 3,073,774, Roberts, a cloth-like plastic mesh is used. In these types of devices, feeding liquid over the entire screen often imposes undesirable design constraints on the frame and conduit structure of the cell.
An additional approach allowing for small points of liquid input and output is shown in U.S. Pat. No. 3,520,803, Ianconelli, in which flat sheets having a cut out or etched central portion defining a tortuous path are employed as spacers. These, however, have the disadvantage of reducing the active membrane area, are subject to high pressure drops, and are fragile and thus, difficult and expensive to manufacture.
The present invention is designed to overcome the above problems by providing a screen which is easy and inexpensive to manufacture while maintaining close tolerances, which allows for point to point liquid input and output which maximizes membrane exposure to fluid flow and, above all, allows for any desired pattern of fluid flow at minimum pressure dropss as may suit the particular application at hand. Accordingly, these and other features and advantages of the invention will become more obvious from the summary below.